This invention relates in general to the construction of steel drums and in particular to a new and useful construction of a heatable winding drum of steel for the manufacture of plastic tubes and receptacles.
Prior art winding drums comprise a cylindrical steel wall which, prior to winding on of the strip material, is heated. The strip material also is heated up to a foamable state and may be wound on a heated steel wall, for example, immediately after being extruded. The heating is intended to improve the quality of the wound tubes or receptacles. What is disadvantageous in this direction is that the cylindrical steel wall cools down relatively rapidly, whereby the quality of the produced wound tubes or receptacles is affected. In fact, to obtain the best quality as to strength and stability, a relative slow cooling down of the steel wall is required. In addition, a relatively large amount of energy is needed for heating up the drum, just because of the rapidly cooling steel wall.
To avoid these drawbacks, a winding drum has been provided having a cylindrical steel wall coated on the outside with rubber or a rubber-elastic plastic. Such an outer coating provides a satisfactory thermal insulation toward the outside. This results in saving energy for heating the cylindrical wall of the drum, and at the same time in a retarded cooling of the cylindrical wall of the drum which still is made of steel.